The y region of bacteriophage lambda is destined to become one of the most thoroughly understood sites of transcriptional control. Leftward transcription for lambda repressor synthesis is initiated in this region at a promoter site called pE. The lambda cII and cIII proteins activate transcription from pE. Rightward transcription for expression of lambda lytic functions starts several hundred nucleotide pairs to the left of the y region, and must proceed through the terminator site tR1 within the y region if lytic functions are to be expressed. The lambda N protein prevents termination from occurring at tR1. (The tR1 site is about thirty nucleotides to the left of pE.) The complete nucleotide sequence of the y region has been determined and the sequence changes of mutants in the y region have been elucidated. My major objective is to continue the basic genetic studies which underlie all investigations of the y region. A particular goal is to isolate more mutants in the "cyr" region, which lies within the y region. The cyr region has a number of important properties. It is (1) the polymerase recognition region of the pE promoter, (2) a probable binding site for the cII protein, (3) a region of inverse symmetry (in twelve of fourteen base pairs) with the tR1 termination region, and (4) a portion of the N-terminal region of the cII gene. This region provides an unusual opportunity for genetic study because it is possible to isolate mutants in the cyr region which alter the cII protein without affecting the pE promoter. It should therefore be possible to determine which base changes within a polymerase recognition region do and which base changes do not inactivate the promoter site. This, in turn, should allow us to conclude whether the inverse symmetry properties of this region are important for polymerase recognition.